In EP 1 280 885 A1 the separation of mammalian cells, insect cells and botanical cells from cell suspension is achieved by using a hydrocyclone.
The typical hydrocyclone described therein consists of a tapered part/cone and an upper cylindrical part, which comprises an inlet for tangential feed in the suspension. The cylindrical part is closed by a top, which comprises in the middle an opening at the top, the overflow. The cone of the hydrocyclone ends with an outlet, the underflow. The hydrocyclone has no moving parts, it operates automatically and it has a long durability. The conventionally domain for using hydrocyclones is to concentrate suspensions, wherein coarse grained drain off the device in form of concentrated suspension at the underflow of the hydrocyclone. The fine particles, which are not separated, leave the hydrocyclone in form of a diluted suspension at the opening at the top of the apparatus, the overflow.
The initial suspension is fed tangentially into the inlet of the hydrocyclone, which is generally at the cylindrical part of the hydrocyclone. The suspension starts to spin within the hydrocyclone. As the suspension begins to move down the tapered section of the hydrocyclone, it accelerates. The cell material, having typically a higher density than the rest of the suspension, moves to the outside wall and leaves the hydrocyclone through the outlet at the underflow. The rest of the suspension is recovered through the opening at the top of the hydrocyclone.
In EP 1 280 885 A1 a hydrocyclone is used in a perfusion system wherein the repatriated cell material leaves the underflow of the hydrocyclone uncontrolled into the bioreactor/collection vessel. The cell material bounces with the maximum velocity onto the surface of the suspension inside the bioreactor. This may lead to high and unphysiological shearing stresses/forces, which can affect the viability and the productivity of the cells negatively.
It may also occur that a sudden decrease of pressure resulting in a sudden expansion/relaxation at the end of the outlet/underflow of the hydrocyclone or a large pressure difference between the inlet and the outlet affects the viability of the cell material negatively. Due to the sudden pressure decrease by emitting the suspension of the underflow back to the suspension in the bioreactor causes high shearing forces to the sensitive cell material, which are responsible for degrade the viability of the cells.